grab ref to x/y axis using Axes.getFromId instead of _plots
grab ref to x/y axis using Axes.getFromId instead of _plots

- looks like fullLayout._plots does not get updated properly
  on resize. Fixing that deserves a PR of its own.
- this commit reverts to the pre-#575 behavior

asolagmbh/plotly.js,aburato/plotly.js,etpinard/plotly.js,etpinard/plotly.js,iongroup/plotly.js,aburato/plotly.js,asolagmbh/plotly.js,iongroup/plotly.js,iongroup/plotly.js,plotly/plotly.js,plotly/plotly.js,plotly/plotly.js,plotly/plotly.js,asolagmbh/plotly.js,etpinard/plotly.js